If you're streaming an MKV file to an Apple TV and are hearing static/digital static audio, you may have Dolby Digital set to 'On' within your Apple TV. On displays and televisions that don't properly support Dolby Digital, you will hear garbled/static audio. To resolve this issue, you'll want to set the Dolby Digital to auto. We've listed instructions below. 

Within your Apple TV menu, access Settings>Audio & Video>Dolby Digital.